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Subject: Re: Search behavior in a case of root fail high/low

Author: Sergei S. Markoff

Date: 23:28:43 03/11/04

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Hello!

>In MTD(f), of course >alpha but <beta is not even possible.

Yes, MTD(f) null-move work is like if we use null-move search result if it's
>alpha but <beta. In practice, I tried it some time ago, it causes a big
disadvantage. I see two problems with it:
1. It increases search instability. Null moves more frequently appears in PV
nodes.
2. It causes more zugzwang problems. And a cost of this problems in average is
much more than in non-PV nodes.

>I have no idea what Fritz does, but I have a primitive technique
>which at least helps in some simple cases:  I don't allow null
>moves in positions where the side to move has very few safe
>pseudo-legal moves.

I have heard about efficiency of scheme in which exact two zero moves in a row
are allowed. In one hand it can help us in a lot of zugzwang positions, but
anyway it causes stronger search degeneration. But I think there are ways to fix
this problem particularly.

>This is another technique I have experimented with, but the last time
>I tried it didn't work very well.

I'm still in thought about this part. I'm not sure that my scheme works well. We
can discuss some more details by e-mail, if you want.

Best wishes,
Sergei



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